The danger of HT batteries

[Refugee]

Originally Posted by derek.ireland

having worked on car electics for 25 years its suprising how often you can get a nasy jolt of a 12 volt car battery in damp conditions .not lethal but makes the hand twitch

You must mean the spark plug leads
The battery will just be a bit uncomfortable to touch like they were in my old cars when I was young.
Try touching a cow fence

[wd40addict]

Interesting how the Zenith Transoceanic has the *male* on the battery and the socket on flying leads connecting to the radio, thus making accidental contact with 90v much more likely!

What were they thinking of?

[ionburn]

Originally Posted by derek.ireland

having worked on car electics for 25 years its suprising how often you can get a nasy jolt of a 12 volt car battery in damp conditions .not lethal but makes the hand twitch

Years ago I remember getting jolts from my train set on the odd occasion. I did wonder about the inductance in the motor causing a higher voltage than 12 to be present, but it is possible to get a jolt depending on conductance (worst case in which people test batteries with their tongue :/ ). It was amusing when our dog chased cars on the Scalextic track and got zapped by the rails. It did not harm him but he was obviously startled. It's perhaps a good point to point out the vulnerability of animals.

[russell_w_b]

the sensitivity to electricity depends upon whereabouts you make contact with it. I've noticed tingling from an earthed(!) 240V a.c. light-box containing a fluorescent tube when I've rested the insides of my wrists on the corners of the light-box. My wrists were perfectly dry too.

[ex 2 Base]

Back in the 1960's when topping up the electrolyte on locos 110 volt starter batteries we could see little arcs from the hairs underneath our arms, quite a tingling sensation. We had to be very careful with spanners etc, the power available would soon melt a spanner jaw. Never felt any thing on 24 volt shunter batteries, all DMU's and coaches were 24 volt . H&S wasn't a thing those days, once you got a shock you were more cautious next time.Ted

[Philips210]

Originally Posted by Refugee

Try touching a cow fence

I did just that when I was about 8, infact I went to grasp the wire not knowing the result. It was a nasty belt and I thought afterwards about why there was a need for all those ceramic insulators along where the posts were situated. I soon realised why! I obviously steered clear of any similar looking fences thereafter.

I am not sure of the typical source impedance for a valve HT battery but would think it is sufficiently low to be a real danger under the wrong circumstances especially if heart problems exist.

I like most have had many belts over the years. The first was from a homemade electromagnet /solenoid which my neighbour (a school teacher) told me how to construct. He didn't however mention the effect of its back emf when the battery was disconnected!

Regards
Symon.

[Refugee]

I can remember playing with a scrap car that still had a battery in it.
I had heard that a dynamo was a glorified motor so with the fan belt removed I tried it and it did indeed spin.
I then tried the same with a pushbike dynamo with a D cell and it just gave me a belt.
It was really an alternator and it had duly let me know.

[Cobaltblue]

I grew up on a farm

I could hold onto Electric fencers it was a competition between me and my cousins, it was worse if you let it just brush you.

When I worked at Liskerard Engineering in the Early 70's (Summer Job) they used to manufacture fencers (Scorpion Brand if I remember correctly) and and I won a bet with the chief Engineer by holding onto one. held the spike with one hand and the output with the other

Wouldn't do it now with an additional 35 Years wear and tear on my heart though

Cheers

Mike T

[stevehertz]

I can see that this thread is morphing rapidly to become yet another "What's the worst electric shock you've ever had" one!

240V mains me, lots of times.

[The Philpott]

Pulse modules that can comfortably produce a multi kV 1/2" spark from a pair of AA alkalines are everywhere, and cheap. Almost worryingly so. Bigclive tried one out on himself (NOT recommended) and it tried to blow him all the way back to Scotland.

The aforementioned 75v button cell stack does indeed give me a mild shock if and when i get in it's way on disconnection from a meter. (Back emf, i think that's the term i was looking for)

Dave

[Philips210]

Originally Posted by Philips210

I am not sure of the typical source impedance for a valve HT battery

Hi

I meant to say internal resistance of the HT battery rather than source impedance.

Regards,
Symon

[Biggles]

I work on telephone lines as part of my day job, and when kneeling on damp grass while connecting lines inside PJL's it's remarkable how nasty 48V can feel, more so when the sharp wires poke into your hands. You just have to hope the line isn't ringing too.
Alan.

[Nanozeugma]

I empathise.
Ever since discovering the hard way that some (insert anglo-saxon vernacular) had "repaired" the broken aerial socket on a live chassis ITT portable TV by bridging the isolation capacitors, without benefit of an isolation transformer.... I have been rather more careful

[mark2collection]

Back in the mid-90's I was bitten by a Barco CRT monitor, one of the professional ones in a metal housing.

I thought I'd satisfactorily discharged the EHT to remove the chassis. One arm behind me, my elbow must have brushed the (metal) cabinet & my thumb slipped under the EHT cap. A very loud click followed by a very loud thump (back of my hand hitting the inside of the cabinet) & a numb arm to follow.

Felt dreadful for the rest of the day, numb arm, felt sick ... mind you, the following day felt great! Appreciation for still being alive perhaps.

I can tell you 32kV's sharpens the mind

Mark

[AC/HL]

It's the current that matters, under extreme conditions as little as 50V can be fatal. Best not chance it!
https://www.quora.com/How-many-volts-will-kill-you

[mark2collection]

It's the volts that give you the jolts, the amps give you the cramps, the frequency?

Hertz!

(Its been a long day, off for a lie down)

Mark

[Jon_G4MDC]

"Volts that jolts but mill's that kills" was the traditional hymn

[kalee20]

Originally Posted by Philips210

Hi

I meant to say internal resistance of the HT battery rather than source impedance.

I've used ten cheap PP3's to make a quick 90V, I did measure the internal resistance (by measuring voltage off and on load), it turned out to be 20 ohms or so.

This means up to 4.5A could be drawn, or (applying the maximum power transfer theorem) 203W. Obviously not for very long.

Probably a traditional carbon-zinc HT battery in days of yore would be not as good, unless rather bigger.

The idea of a fuse in series is a good idea, it can save an unwanted firework display, even though it won't prevent shocks. But, as has been said, 90V is hardly likely to be fatal.

Oh, and yes I've used the tongue test to see if a battery still has life (but not more than 9V!)

[Refugee]

When I was young the tongue test was known as "tasting" the battery to find out if it was still good.

[Jon_G4MDC]

Once upon a time the 90V battery of my HAC one valver did get wired to the side hinges of my school desk.

The light fingered bully who had been making my life hell for months squawked quite a bit when he encountered it. He blubbed to the teacher and I got a roasting for it.